This invention relates to an engine having a combustion control system and more particularly to an improved, compact engine design that permits the use of such a combustion control system.
As is noted in the aforenoted copending parent application, it has been found that the performance of an engine can be significantly improved by appropriately selecting the ratio of area of the intake passage between the throttle valve and the intake valve seat or port and the exhaust volume of the combustion chamber. The exhaust volume is the displacement volume of the cylinder when the piston at bottom dead center position. If this ratio is appropriately selected relative to the valve overlap period, internal exhaust gas recirculation can be optimized and stable lean burn running can be achieved.
In order to obtain the optimum ratio of these respective volumes, which ratio preferably is in the range of 0.15 to 0.45, it is necessary to position the closed condition of the throttle valve quite close to the intake valve seat. Optimally, this could be accomplished by rotatably journaling the throttle valves directly in the cylinder head. However, this is not practical for many reasons. Therefore, the throttle valves are normally positioned in one or more separate throttle bodies that are affixed to the side of the cylinder head. This tends to increase the volume of the intake passage to such an extent that the desired ratio cannot be maintained.
It is, therefore, a principal object of this invention to provide an improved, compact and nevertheless separate throttle body arrangement for an internal combustion engine.
It is a further object of this invention to provide an improved throttle valve and throttle body construction for an engine wherein the throttle body can be positioned so that the throttle valve in its closed position is disposed within a plane that extends parallel to the axis of the cylinder bore and which contains the outer peripheral edge of the cylinder head.
In addition to the desirability of maintaining the aforenoted ratio, there are also a number of other reasons why it may be desirable to position the throttle valve in close proximity to the intake valve seat. Where the engine has multiple cylinders, this frequently necessitates the use of multiple throttle bodies in order to maintain this relationship.
It is, therefore, a further object of this invention to provide a multi-cylinder engine having multiple throttle bodies and wherein the throttle bodies are positioned so that there respective throttle valves, when in their idle positions, are disposed inwardly from a plane parallel to the axis of the cylinder bore and containing the outer peripheral edge of the cylinder head on the intake side.
Where the throttle bodies and throttle valves are positioned in close proximity to the cylinder head, this may give rise to some additional difficulties in placement and operation of other components. For example, it is necessary when utilizing multiple throttle bodies to have a synchronizing mechanism so that the throttle valve shafts all operate in unison and have the desired relationship. It is also necessary to employ the mechanism for operating the throttle valves. The placement of this operating mechanism can be complicated when the throttle valves are positioned in such close proximity to the cylinder head.
It is, therefore, a still further object of this invention to provide an improved throttle valve arrangement and an actuating mechanism for actuating the throttle valve that is more freely accessible.
It is a still further object of this invention to provide an improved throttle valve actuating mechanism wherein the throttle valve shafts are operated by a separate throttle valve actuating shaft that is journaled for rotation about an axis parallel to but spaced from the axes of the throttle valve shafts.
The problems of throttle synchronization and throttle valve actuation are further complicated when the engine is provided with one or more overhead camshafts. Since the camshafts are driven at one-half crankshaft speed, a speed reducing mechanism must be employed between the crankshaft and the camshafts. This is normally done by sprockets that are driven by one or more flexible transmitters either chains or belts.
The size of these sprockets and their mounting in the cylinder head tends to enlarge the overall size of the cylinder head. In fact, the sprocket drive frequently will lie over and outwardly of the throttle valves when they are placed in the desired location close to the intake valve seats. This presents still further difficulties in connection with the placement and operation of the throttle actuating mechanism.
Also, it is frequently the practice to employ a control system for the engine that requires an input information from a throttle position sensor. The positioning of this sensor is also complicated by the close positioning of the throttle valves to the intake valves.
It is, therefore, a still further object of this invention to provide an improved arrangement for providing a compact engine construction and which accommodates a throttle position sensor associated with at least one of the engine throttle valve shafts.
In connection with the combustion control system for an engine it has also been the practice to employ fuel injection. Fuel injection permits more accurate control of the amount and timing of fuel delivery than carburetors. In addition, it is much easier to adapt the fuel injection to transient conditions than with carburation.
Where fuel injection is employed and the fuel is injected into the intake passage, the accuracy of the amount of fuel injected can be improved significantly if the fuel is delivered at a pressure that is related to the induction system pressure so that a predetermined pressure relationship exists between the injection pressure and the induction system pressure.
It is, therefore, a still further object of this invention to provide improved arrangement for controlling the fuel supply pressure to a fuel injector that injects into an induction passage so that a predetermined pressure differential exists between the injection pressure and the induction system pressure.
In spite of the advantages of fuel injection, there is a problem as to the depositing of fuel on either the intake passage or portions of the intake system or on the walls within the combustion chamber. Sometimes it is not desirable to have such fuel deposition. However, at other times it is desirable to deposit the fuel, particularly on the walls of the intake system. By so depositing the fuel, acceleration performance can be improved when operating in transient conditions from a given speed to an increased speed or power output.
With manifold type injection, this has been attempted to be accomplished by spraying fuel on the intake valve. However, this is not a particularly desirable expedient because of the fact that the flow across the intake valve may not be uniform and in fact may be desired to be non-uniform under some running conditions.
It is, therefore, a still further object of this invention to provide an improved fuel injection system wherein the fuel can be injected onto a wall of the throttle valve so that when the throttle valve position is changed, the flow across the throttle valve will sweep the fuel into the intake mixture more uniformly and more rapidly.
When this is done, however, the strategy of injection timing should be different when the engine is operating under load and transient conditions rather than when it is not operating under a load and when there are transient conditions. It is, therefore, yet another object of this invention to provide an improved fuel injection system wherein the fuel injection is varied under transient conditions and the amount of variance is changed depending upon whether the engine is operating under a load or not.